The prior art indicates that polyurethane foams made from phosphate polyols have desirable fire properties, but achieving this property requires replacing all of the polyol originally used in the foam formulation with the phosphate polyol. This high level of substitution is uneconomic and may negatively impact foam physical properties. The prior art also indicates that phosphate polyols may be incorporated into aqueous emulsions as components of fire retardant polyurethane coatings. While phosphorus-containing fire retardants are well known in the art of polyurethane foam, a need exists for low-viscosity materials which are effective at use levels comparable to those of current state-of-the-art fire retardants, as well as for low-viscosity non-halogenated materials with both burning and thermal stability performance comparable to that of current halogenated fire retardants.
While numerous non-halogen phosphorus-containing fire retardants for rigid polyurethane foam are known, the prior art provides essentially no guidance on how to optimize the fire retardant for both fire and char performance while maintaining convenient handling properties and use levels comparable to those of conventional halogenated phosphates.
The following United States patents provide the background of the invention:
The addition of propylene oxide to phosphoric acid while controlling temperature below 95 F (35 C) resulted in a phosphate ester (U.S. Pat. No. 2,372,244).
The addition of more than three moles of alkylene oxide on average per phosphate hydroxyl requires boron and tin catalysts (U.S. Pat. No. 3,317,638).
The preparation of phosphate polyols from phosphoric acid containing 12-28% water requires subsequent water removal to be suitable for rigid polyurethane foam applications (U.S. Pat. No. 3,317,639).
The preparation of phosphate polyols from phosphoric acid and halogenated epoxides including epichlorohydrin has been disclosed (U.S. Pat. No. 3,281,502). Phosphate polyol use levels are high, from 40-85 wt % of the overall polyol mass.
The addition of phosphoric acid to alkylene oxides for use as polyurethane flame retardants involves a highly exothermic reaction, which is difficult to manage on an industrial scale (U.S. Pat. No. 3,393,254).
Phosphate polyols can be prepared from phosphoric acid and alkylene oxides in the presence of polyether polyols, but extended reaction times are required and the phosphorus content is very low, less than about 2% (U.S. Pat. No. 3,639,543).
Phosphate polyols derived from the reaction of ethylene oxide with phosphoric acid are known as components of fire retardant rigid polyurethane foams (U.S. Pat. No. 4,051,082). The polyurethane foams prepared from the inventive phosphate polyols require high isocyanate index and 15-80 wt % of the phosphate polyol relative to total polyol.
Phosphate esters lacking hydroxyalkyl functionality will not react readily into polyurethane foams (U.S. Pat. No. 6,512,133).
Phosphate polyols can be incorporated into polyurethane prepolymer-based aqueous emulsions for use as flame retardant coatings (U.S. Published Patent Application No. 2013/0203936).
Polyols of the present invention can be combined with phosphorus-based fire retardants. Examples of phosphorus compound used in fire retardants include U.S. Pat. No. 9,023,925 to Qi, Phosphorus-Containing Flame Retardants for Polyurethane Foams; U.S. Pat. No. 9,718,937 to Dai, Inherent Flame Retardant Rigid Polyurethane Foam; U.S. Pat. No. 8,846,967 to Hansel, Process for Preparing Alkyl Phosphates; and U.S. Pat. No. 8,703,853 to Kasowski, Flame Retardant and Compositions Containing It; the disclosure of each of which is incorporated herein.